1. Field of the Invention
The present invention relates to an apparatus for producing synthetic resin moldings or rubber moldings in an atmosphere of reduced pressure in a vacuum chamber, and the apparatus is particularly suitable to make polyurethane foams, for example automotive steering wheel coverings, steering wheel pads, etc., by reaction injection molding (RIM hereinafter) in the atmosphere of reduced pressure in the vacuum chamber.
2. Description of Related Art
Heretobefore, in the field of producing sysnthetic resin moldings, an atmosphere of reduced pressure is generally made by a vacuum ppot 51 which is shown in FIG. 6. (See Japanese Patent Laid-open publicatoin No. Sho 62-164709.) For example, a molding container 52 is located in the vacuum pot 51. A polyurethane material which includes water as a blowing agent is poured into the molding container 52. A lid 53 of the vacuum pot 51 is closed, and the vacuum pot 51 becomes airtight. Then, the vacuum pot 51 is vented to an atmosphere of reduced pressure by a vacuum pump 54, and the polyurethane material is foamed.
However, if RIM is carried out in the vacuum pot 51, it is necessary to contact an injection nozzle of a mixing head of an injecting mechanism (not shown) with a mold, such as molding container 52, in the vacuum pot 51 through the wall of the vacuum pot. In such a case, a sealing mechanism between the vacuum pot and the injection nozzle, moves along wich movement of the vacuum pot in an upward and downward direction. The injection nozzle itself will slide into and out of that sealing mechanism. This is a very intricate structure. Also, before and after RIM operations, the vacuum pot must move, relative to the mold, for example, downwardly, to expose and open the mold and upwardly to close the mold.
In such a case, there are some problems. Many attachments are necessary, and that increases the cost of the apparatus. Also, preservation of the apparatus is a problem because of the intricate sealing mechanism.
Therefore, we preliminarily proposed to provide an apparatus which had a vacuum box comprising a divided upper casing and a divided lower casing, and a mold which is surrounded by the vacuum box to an airtight situation. (See Japanese Patent Laid-open publication No. Hei 04-226313, which is now filed in the U.S. patent application Ser. No. 08/268,661, now U.S. Pat. No. 5,464,582.)
However, this apparatus has a remaining problem which is that it is difficult to change the mold, especially since the mold is surrounded in the vacuum box.
The present invention has been developed to overcome the problems associated with the conventional apparatus described above. An object of the present invention is to provide apparatus havine a vacuum chamber, wherein the changing manner of the mold can be improved. Another object of the present invention is to provide apparatus, wherein the sealing mechanism of the vacuum chamber or the injection nozzle is simple. The other object of the present invention is to provide apparatus, wherein the cost of the apparatus is reduced, and preservation of the apparatus is improved.